Growth,phenology, and biomass allocation of alien Solidago species in central Europe

Plant invasion is a major threat to the integrity of an ecosystem. Exceptionally successful invaders in Europe are the American species of Solidago genus. In this study we examined growth, reproduction, and phenology of Solidago species, of American origin, growing in central Europe (S. altissima, S. canadensis, S. gigantea, S. graminifolia). These taxa were compared with two native species: Solidago virgaurea and Tanacetum vulgare. We observed high differentiation in height, number of shoots, and biomass production between individuals within taxa. Generally, the invasive species produced substantially (two to five times) more biomass than the native ones, being statistically significant in the comparison of alien Solidago graminifolia and S. gigantea versus native S. virgaurea and T. vulgare. The ratio of biomass of reproductive parts to overall biomass varied considerably among years, but generally the lowest one was for Solidago altissima, and the highest for S. graminifolia. It shows a lack of a clear pattern of differentiation between alien and native species in terms of biomass investment in reproduction. We observed a general tendency of allocation of a major part of biomass in rhizomes by phalanx species (S. graminifolia and S. gigantea), while species with guerrilla strategy (S. altissima and S. canadensis) invested more biomass in stems and leaves. However, because of the high variability there was no clear, stable pattern of statistically significant differences between these two groups. The results suggest that S. graminifolia reveals a strong potential of invasion, in spite of its, so far limited, distribution in Europe.     

Strong regeneration ability from rhizome fragments in two invasive clonal plants (Solidagocanadensis and S. gigantea)

The two rhizomatous perennials Solidago canadensis and S. gigantea belong to the most widespread alien plants in Europe. Anecdotal observations suggest that they disperse also by rhizome fragments. For testing their resprouting ability, rhizome fragments of different sizes from both species were buried at four different soil depths (0, 5, 10 and 20 cm, respectively) in a common garden. Rhizome fragments of S. canadensis ranged 3–6 cm in length, those of S. gigantea 5–20 cm in length. Resprouting plants were harvested after 3 months and growth related traits measured to assess their vitality. Resprouting rate in S. gigantea was far higher than in S. canadensis (85 and 19%, respectively). In S. gigantea, fragments of all sizes resprouted from all soil depths whereas none rhizome of S. canadensis emerged from 20 cm burial depth. In S. gigantea, size related traits showed significant interactions between fragment size and burial depth, but not relative shoot growth rate. At all burial depths, vitality of plants emerging from small rhizomes was lower than plants emerging from large rhizomes. Effects of rhizome size became stronger with increasing burial depth. The results show that both species are able to resprout from buried rhizome fragments, and that succesful regeneration is more likely to occur in S. gigantea. Managing these species should avoid any activities promoting rhizome fragmentation and dispersal of fragments.     

“黄莺花”与一枝黄花及其同属近缘种的形态比较

形态上与入侵杂草加拿大一枝黄花十分相似的“黄莺花”,近来作为鲜切花的配花走俏花卉市场,也引起了社会对其管理的高度关注。本文通过比较市售8个批次的“黄莺花”与35个入侵中国的加拿大一枝黄花种群、原产地的一枝黄花属2个种群以及一枝黄花的叶和花的11个形态学特征,并进行聚类分析。结果表明除第5批 “黄莺花”外的7个批次单独聚为一类,第5批次与35个入侵中国的加拿大一枝黄花种群聚为一大类,再结合加拿大的2个种群,而一枝黄花单独为一类。这充分说明“黄莺花”并非一枝黄花,而与入侵我国的加拿大一枝黄花各种群接近。进一步再与巨大一枝黄花和粗糙一枝黄花特征相比较分析,发现“黄莺花”与粗糙一枝黄花聚在一组,并进一步与入侵的加拿大一枝黄花相聚,加拿大1和2的种群更接近巨大一枝黄花,而一枝黄花单独成为一支。无论是加拿大一枝黄花、粗糙一枝黄花还是巨大一枝黄花都属于“加拿大一枝黄花复合种”。由此可以认为市售“黄莺花”属于外来入侵杂草加拿大一枝黄花的复合种。叶片长宽比、离基三出脉距叶基距离、表皮毛数的多少、缘花/盘花比等是“黄莺花”与该属其它类群分类鉴定的重要形态学特征性指标。     

GENETIC DIFFERENTIATION AMONG HOST-ASSOCIATED POPULATIONS OF THE GALLMAKER EUROSTA SOLIDAGINIS (DIPTERA: TEPHRITIDAE)

Eurosta solidaginis, a gallmaking tephritid (Diptera), infests at least two species of Solidago in the eastern United States. We used horizontal starch gel electrophoresis of enzymes to examine whether populations on the two principal host plant species, Solidago altissima and S. gigantea, have diverged genetically. At the d -β-hydroxybutyrate dehydrogenase (HBDH) locus, the predominant allele in all nine populations from S. altissima (HBDH^1.00) was absent or uncommon in all but 1 of the 12 populations from S. gigantea. At the phosphoglucomutase locus (PGM), the most common allele in all populations was PGM^1.00, but the frequency of this allele was, with one exception, higher in populations from S. gigantea than in populations from S. altissima. Genetic heterozygosity was usually greater in populations from S. altissima (H? = 0.028) than in populations from S. gigantea (H? = 0.009). A phylogenetic tree derived from a genetic distance matrix clustered gallmaker populations from the same host plant together.     

MITOCHONDRIAL DNA PHYLOGEOGRAPHY OF HOST RACES OF THE GOLDENROD BALL GALLMAKER,EUROSTA SOLIDAGINIS (DIPTERA: TEPHRITIDAE)

We determined the phylogenetic relationships and geographic distribution of mitochondrial haplotypes of two host races of the tephritid fly Eurosta solidaginis, a gallmaker that attacks species of goldenrod (Solidago). We performed a preliminary survey by sequencing 492 bp from the 3′ ends of the mitochondrial cytochrome oxidase I and II subunits from a single individual from eight S. gigantea- and 10 S. altissima-associated populations across their range in eastern North America and from two outgroup species, Eurosta comma (two populations) and E. cribrata. Eurosta solidaginis haplotypes fell into two groups (“E” and “W” clades), which differed by four substitutions, one of which occurred within the recognition site of the DdeI restriction enzyme. We used the presence or absence of the restriction site to survey a total of 11 S. gigantea (20 individuals) and 20 S. altissima (43 individuals) host-race populations. All gigantea-fly haplotypes regardless of geographic origin carried the E-clade haplotype, whereas altissima-fly haplotypes were geographically partitioned. Altissima flies east of Michigan were of haplotype E, whereas those west of Michigan were of haplotype W, with mixed populations found in lower Michigan. These patterns confirm an earlier allozyme survey that suggested that S. altissima is the ancestral host for the gallmaker, but also suggest that the gigantea fly populations were derived from eastern U.S. altissima fly populations. The data support the conclusions of behavioral and ecological studies indicating that the shift to the derived host was facilitated by escape from natural enemies.     

Light reduction predicts widespread patterns of dominance between asters and goldenrods

Here we investigate the long-cited pattern that throughout the eastern United States, Solidago species (goldenrods), and in particular S. canadensis displace Aster species and dominate old-field communities. Theory predicts that such a ubiquitous pattern of repeated dominance should be linked to competitive ability for a limiting resource. However, no one has investigated this possibility in old-fields, representing a potentially significant gap in our understanding of a common human-altered environment. We tested the hypothesis that S. canadensis is the superior competitor for light compared to other common co-occurring goldenrod species, and that the goldenrods in general are the superior competitors for light compared to coexisting aster species, which are typically less abundant. We tested this hypothesis by comparing the light attenuation abilities of four goldenrod species, S. canadensis, S. rugosa, S. gigantea, and Euthamia graminifolia, and three aster species, Aster novae-angliae, A. pilosus, and A. prenanthoides. Consistent with our hypothesis, S. canadensis had a greater ability to attenuate light than any of the other goldenrods at higher densities, and the goldenrods overall had a greater ability to attenuate light than the asters. By conducting a census in our study area, we verified that S. canadensis is locally the most abundant goldenrod and that goldenrods are more locally abundant than asters. Furthermore, by conducting a literature survey we found evidence that S. canadensis replaces A. pilosus through time. Thus we found a close correspondence between relative abundance in the field and light attenuation ability in field experiments. These results are consistent with theory predicting that competition for limiting resources, in this case light, explains patterns of dominance and relative abundance in old-field plant communities.     

Manipulation of cytosine methylation does not remove latitudinal clines in two invasive goldenrod species in Central Europe

Invasive species frequently differentiate phenotypically in novel environments within a few generations, often even with limited genetic variation. For the invasive plants Solidago canadensis and S. gigantea, we tested whether such differentiation might have occurred through heritable epigenetic changes in cytosine methylation. In a 2‐year common‐garden experiment, we grew plants from seeds collected along a latitudinal gradient in their non‐native Central European range to test for trait differentiation and whether differentiation disappeared when seeds were treated with the demethylation agent zebularine. Microsatellite markers revealed no population structure along the latitudinal gradient in S. canadensis, but three genetic clusters in S. gigantea. Solidago canadensis showed latitudinal clines in flowering phenology and growth. In S. gigantea, the number of clonal offspring decreased with latitude. Although zebularine had a significant effect on early growth, probably through effects on cytosine methylation, latitudinal clines remained (or even got stronger) in plants raised from seeds treated with zebularine. Thus, our experiment provides no evidence that epigenetic mechanisms by selective cytosine methylation contribute to the observed phenotypic differentiation in invasive goldenrods in Central Europe.     

The effects of host race, gender, and host plant distribution on alighting behavior, mating, and oviposition in Eurosta solidaginis

Eurosta solidaginis Fitch (Diptera: Tephritidae) has formed host races on Solidago altissima L. and Solidago gigantea Ait. (Asteraceae), and reproductive isolation between these host races is brought about in part by host‐associated assortative mating. Any non‐assortative mating creates the potential for gene flow between the populations, and we investigated the conditions that favored non‐assortative mating. We hypothesized that the frequency of non‐assortative mating would be influenced by differences in the behaviors of the host races and sexes and by the presence and pattern of distribution of the two host species. To test these hypotheses, we caged flies on four combinations of 32 potted host plants: all S. altissima, all S. gigantea, and cages with both host species arranged in either two pure species blocks or randomly dispersed. We recorded the number of flies of each host race that alighted on each host species and the frequency of mating within and between the host races. Males of both host races were observed on plants more frequently than females. Flies of the host race from S. gigantea (gig flies) were observed on plants in greater absolute numbers, and they mated more frequently than flies of the host race from S. altissima (alt flies). In all treatments, gig flies of both sexes were found on non‐natal host plants significantly more frequently than alt flies, and gig females showed a weaker preference for their host species than did gig males or alt flies of either gender for their respective natal hosts. Assortative mating predominated in all treatments, and flies from each host race mated more frequently in cages containing their own host plant. The frequency of non‐assortative mating varied among treatments, with the matings between alt ♀ × gig ♂ being more common in the pure S. altissima treatment and the gig ♀ × alt ♂ being more frequent in the pure S. gigantea and random treatments. Matings between gig ♂ × alt ♀ were more common overall than the reciprocal mating, because gig males were more active in pursuing matings and in alighting on the non‐natal host plant than alt flies. Non‐assortative matings were more frequent in the random than in the block treatments, but this difference was not significant. Because of strong selection against oviposition into the alternate host, we hypothesized that host plant distribution would not affect oviposition preference. We tested this hypothesis by examining the oviposition behavior of naïve, mated females in two treatments in which both host species were present: either arranged in blocks or randomly dispersed. Females oviposited only into their natal host, regardless of host plant distribution.     

Gall Flies, Inquilines, and Goldenrods: A Model for Host-race Formation and Sympatric Speciation

Host shifts and subsequent host-race formation likely play amore common role in the speciation of herbivorous insects thanhas generally been recognized. Our studies of the interactionsof goldenrod host plants (Solidago: Compositae), the gall flyEurosta solidaginis (Diptera: Tephritidae), and the stem- andgall-boring Mordellistena convicta (Coleoptera: Mordellidae)provide behavioral, ecological, and genetic evidence of insecthost races that may represent incipient species formed via sympatricspeciation. Eurosta solidaginis has developed genetically differentiatedand reproductively isolated host races that are associated withthe ancestral host Solidago altissima and the derived host S.gigantea. Conventional wisdom suggests that shifts even to closelyrelated host plants are limited by host preferences or the inabilityto utilize a chemically and developmentally distinct host. However,our preliminary work with Eurosta from S. gigantea implies thathost choice and gall induction do not deter a shift to S. canadensis.The galling of Solidago by Eurosta created a new resource thathas led to a subsequent host range expansion by the stem-boringbeetle. Mordellistena convicta from stems and galls are geneticallydistinct and likely shifted from stems to galls. Beetles fromS. altissima versus S. gigantea galls exhibit assortative matingand higher preference for and/or performance on their natalhost. The present-day distributions of the Eurosta host racesand their behavioral isolating mechanisms do not suggest thatgeographic isolation was required for their formation; ratherthese characteristics suggest a sympatric mode of differentiation.Our findings lend credence to recent assertions that sympatricspeciation may be an important source of biodiversity.     

BEHAVIORAL EVIDENCE FOR HOST-RACE FORMATION IN EUROSTA SOLIDAGINIS

We report behavioral evidence that Eurosta solidaginis, a stem-galling tephritid fly, has formed host races on its two goldenrod hosts, Solidago altissima and S. gigantea. Previous work has shown that flies from each host plant differ electrophoretically at the level of host races. The two host-associated populations were truly sympatric and were frequently found on host plants of the two species growing interdigitated with each other. Each host-associated population demonstrated a strong preference for ovipuncturing its own host. The S. gigantea–associated population emerged 10 to 14 d earlier than the S. altissima–associated population, contributing to the reproductive isolation between populations. Partial reproductive isolation is also maintained by a preference for mating on the host from which the fly emerged. The populations meet the criteria established for host races, suggesting that they may be in an intermediate stage of sympatric speciation.     

Long-term suppression of insect herbivores increases the production and growth of Solidago altissima rhizomes

Summary Although insect herbivores have many well documented effects on plant performance, there are few studies that assess the impact of above-ground herbivory on below-ground plant growth. For a seven year period in which no large-scale herbivore outbreaks occurred, a broad spectrum insecticide was utilized to suppress herbivorous insects in a natural community dominated by Solidago altissima. Ramet heights, rhizome lengths, rhizome biomass, and the number of daughter rhizomes all were lower in the control plots than in the insecticidetreated plots. These effects should lead to a decrease in the fitness of genets in the control plots relative to the fitness of genets in the insecticide-treated plots. We also found that ramets in the control plots appear to have compensated for herbivory: the ratio of rhizome length to rhizome biomass was greatest in the control plots, which indicates that clones moved farther per unit biomass in these plots than in the insecticide-treated plots. Clonal growth models show that this shift in allocation patterns greatly reduced the magnitude of treatment differences in long-term clonal displacements.Previous work has shown, and this study verified, that clonal growth in S. altissima is well represented by random-walk and diffusion models. Therefore, we used these models to examine possible treatment differences in rates of clonal expansion. Although rhizome lengths were greater in the insecticide-treated plots, results from the models suggest that our treatments had little impact on the short- and long-term displacement of S. altissima ramets from a point of origin. This occurred because S. altissima ramets backtrack often, and thus, treatment differences in net displacements are less pronounced than treatment differences in rhizome lengths.     

Systematic study of the Altissimae and Giganteae species groups of the genus Vernonia (Compositae)

Morphological variation within and between the taxa of the Altissimae (Vernonia altissima, V. ovalifolia, andV. flaccidifolia) and Giganteae (V. gigantea) was investigated. The data for these studies were obtained from population samples, herbarium specimens, and greenhouse-grown transplants. The taxa were hybridized in all possible combinations, and F₂ progeny were produced fromV. altissima XV. ovalifolia F₂’s. Fertility in the hybrids was estimated by examination of chromosome pairing at meiosis and by pollen stainability. It is concluded thatVernonia altissima should be regarded as a synonym ofV. gigantea and thatV. ovalifolia should be reduced to subspecific rank asV. gigantea ssp.ovalifolia. The evolution of the two subspecies ofV. gigantea is discussed.Vernonia flaccidifolia is maintained at the species level.     

Comparative ecophysiology ofChrysanthemum pacificum Nakai andsolidago altissima L. 1. whyS. altissima cannot be established on the seashore

A fieldsurvey was made to elucidate whether salt spray is a major factor in preventing a common inland weed,Solidago altissima, from being established on the seashore of Boso Peninsula. Seasonal changes in the intensity of salt spray, sodium content in the soil water and soil water contents were measured at the seashore and inland. Seeds ofS. altissima were sown at both sites with those of a common maritime species,Chrysanthemum pacificum. The number of surviving shoots of the seedlings were periodically counted for 1 year. The intensity of the salt spray, sodium content and water contents of the soil on the seashore fluctuated seasonally. There were some periods when the intensity of salt spray was comparable to that of the inland site. Most of theS. altissima seedlings survived at the inland site. AllS. altissima seedlings germinated at the seashore were completely eliminated. The death rate ofS altissima seedlings at the seashore was not constant. Ninety-five percent of theS. altissima seedling in total died out during the four periods of intensive salt spray. The death rate ofC. pacificum seedlings on the seashore was not especially high during those periods. Correlation between seasonal changes in the death rate ofS. altissima seedlings and the sodium content or water content of the soil was low. These results indicate that intensive salt spray, intermittently blown in from the sea, is one of the most critical environmental factors that eliminatesS. altissima from the seashore.     

草甘膦对入侵植物加拿大一枝黄花和伴生植物白茅光合特性的影响

入侵植物加拿大一枝黄花(Solidago canadensis)给许多地区带来了较大危害,目前常采用化学防除法进行防除,但除草剂防治入侵植物的同时难免会影响土著植物的生长。为探讨草甘膦对入侵植物与本地植物光合特性的影响,以加拿大一枝黄花及其伴生种白茅(Imperata cylindrica)为研究对象,采用盆栽控制试验方法,研究不同浓度草甘膦处理21后单种、混种加拿大一枝黄花和白茅的生长特征及光响应过程。结果表明:1)草甘膦显著抑制两种植物的生长。随处理浓度升高,加拿大一枝黄花的株高增长量不断减小、叶片枯萎率不断增加;白茅的分蘖死亡率、叶片枯萎率不断升高。白茅对草甘膦较敏感,0.6mL/L浓度下白茅先失绿,1.2mL/L下其分蘖死亡率、叶片枯萎率均超50%;1.8mL/L下加拿大一枝黄花叶片枯萎率超50%。施药后与单种相比,混种加拿大一枝黄花株高增长略快、叶片枯萎率略低,混种白茅分蘖死亡率及叶片枯萎率均较低,但单、混种之间差异不显著。种间关系显著影响白茅的分蘖数。2)随处理浓度递增,加拿大一枝黄花和白茅叶片净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)均不断降低,白茅下降更快。两个物种胞间CO_2浓度(C_i)的变化不同,随着浓度升高,单种加拿大一枝黄花C_i先下降而后上升,而混种时的C_i则不断下降;单、混种白茅C_i均上升。3)草甘膦显著影响加拿大一枝黄花和白茅最大净光合速率(P_(nmax))、光饱和点(LSP)和光补偿点(LCP);对两个物种暗呼吸速率(R_d)的影响不显著,对加拿大一枝黄花表观量子效率(AQY)的影响同样不显著,但显著影响白茅AQY。种植方式显著影响两个物种P_(nmax)、LSP以及白茅R_d和AQY。0.6mL/L草甘膦对混种加拿大一枝黄花和白茅P_(nmax)的影响要大于对单种植株的影响,随处理浓度上升,对不同种植方式下两种植物P_(nmax)的影响趋近。与本地种白茅相比,入侵植物加拿大一枝黄花具有更高的光合速率和生长速率;草甘膦显著降低两个物种的生长和光合作用,白茅对草甘膦处理更敏感。     

Variation in selection pressures on the goldenrod gall fly and the competitive interactions of its natural enemies

Summary Larvae of the tephritid fly Eurosta solidaginis induce ball-shaped galls on the stem of tall goldenrod, Solidago altissima. Survival probability depends on gall size; in small galls the larva is vulnerable to parasitoid oviposition, whereas larvae in large galls are more frequently eaten by avian predators. Fly populations from 20 natural old fields in central Pennsylvania were monitored in 1983 and 1984 to examine the distribution of the selection intensity imposed by natural enemies, the parasitoids Eurytoma gigantea and E. obtusiventris, the inquiline Mordellistena unicolor, and the predatory birds Dendrocopus pubescens and Parus atricapillus. Mordellistena and E. obtusiventris are able to attack galls of all diameters while E. gigantea and the predatory birds preferentially assaulted small and large diameter galls, respectively. Eurosta in intermediate sized galls had the highest survivorship, hence selection had a stabilizing component. However, parasitoid attack was more frequent than bird attack, and the two did not exactly balance, thus there was also a directional component. The mean directional selection intensity on gall size was 0.21 standard deviations of the mean, indicating that larger gall size was favored. Interactions among the insect members of the Eurosta natural enemy guild are complex and frequent.     

The structure of the phytophagous insect fauna on the introduced weed Solidago altissima in Switzerland

Solidago altissima L. was introduced into Europe as an ornamental plant from North America more than 100 years ago and the phytophagous insect fauna of it was recently examined in Switzerland where it has become an important weed in disturbed habitats. Rhizomes and aerial parts were examined and all insects collected in summer were tested in a no-choice feeding test. 18 out of 55 phytophagous insects were found feeding on S. altissima in Switzerland and for the remaining 37 the relation with the plant was not determined. The insects that have expanded their host range to feed on S. altissima since its introduction to Switzerland are almost solely opportunistic, unspecialized ectophages not closely attuned to the growth cycle of S. altissima. Only 4% of the insects were specialists and 9% endophagous. In contrast in North America S. altissima supports 25% specialists and 17% endophages. The native Solidago virgaurea L. in Switzerland supports many more specialists (28%) and endophages (23%) than S. altissima here. Possible reasons why almost none of these have switched to S. altissima are discussed. A comparison is made between the number of insects recruited by S. altissima in Switzerland with the number recruited by the exotic plants Heracleum mantegazzianum Som. & Lev. (Apiaceae) in Switzerland and Xanthium occidentale Bertol. (Asteraceae) in Australia. Reasons for different levels of insect recruitment are discussed. The high number of phytophagous insect species found on S. altissima in North America shows that there should be no shortage of possible control agents and any insects imported into Switzerland for the biological control of S. altissima would find largely unexploited food sources awaiting them.     

Food plant choices of two goldenrod beetles: Relation to plant quality

Summary The leaf beetles Trirhabda borealis and T. virgata are specialist herbivores of meadow goldenrods, Solidago spp., in central New York. Upon emergence, both larvae and adults must actively search for food plants, and must choose among the five goldenrod species (S. canadensis, S. gigantea, S. graminifolia, S. juncea and S. rugosa) that co-occur in old fields. The relationship between Trihabda foraging decisions and plant quality was examined by comparing food preferences in the field with the performance of beetles caged on each host. Trirhabda adults were highly selective in their use of food plants. Adults of T. borealis preferred a single host, S. canadensis, while T. virgata adults were most common on S. canadensis and S. gigantea. These preferences were not strictly related to variation in plant quality. In the laboratory, T. borealis performed equally well on four goldenrods (but completely failed to reproduce when fed S. graminifolia), and T. virgata performed equally well on all five hosts.Larval feeding preferences in each beetle species were broader, and were more in accord with subtle variation in plant quality. Newly-hatched T. borealis larvae readily colonized four hosts and rejected only S. graminifolia, which conferred the lowest survivorship and the slowest growth. Larvae of T. virgata accepted each host, even though growth rates were somewhat slower on S. graminifolia and S. juncea.Ontogenetic differences in host preference and host tolerance may have evolved because of the different host-finding abilities of each beetle stage. During host search, the sluggish, newly-emerged larvae may be more food-limited and accept even marginally inferior food plants. The relatively mobile adults are more discriminating and use a subset of suitable hosts. The intermingled dispersion of Solidago species in old fields results in frequent larval colonization of hosts seldom used by adults. In diverse plant communities, ultimate patterns of food plant choice can be a complex function of at least three factors: intrinisic plant quality, local plant dispersion, and the host-search abilities of the insect forager.     

Reproductive allocation of Solidago canadensis L. plays a key role in its invasiveness across a gradient of invasion degrees

Reproductive allocation (RA) plays a vital role in the development of ecological strategies during the life cycle of plant species. Invasive alien plants (IAP) may exist at various invasion degrees across a gradient of the colonization process with several grades of relative abundances in the occupied environments. The progressive variation in the invasion degree of IAP has the potential to modify their RA strategy. This study purposes of estimating the RA strategy of the IAP Solidago canadensis L. and the correlations among RA of S. canadensis, the invasion intensity of S. canadensis, the invasiveness of S. canadensis, and the community invasibility across a gradient of invasion degrees by using the field sampling experiment. The height and relative abundance of S. canadensis did not remarkably affect its RA. The RA of S. canadensis was positively related to its reproductive biomass and total biomass. The key reason may be that plant individuals with higher total biomass can allocate more resources into sexual reproduction. The RA of S. canadensis was positively related to its invasiveness. Thus, the RA of S. canadensis may be crucial to its invasiveness.     

Evolutionary patterns in the antR-Cor gene in the dwarf dogwood complex (Cornus, Cornaceae)

The evolutionary pattern of the myc-like anthocyanin regulatory gene antR-Cor was examined in the dwarf dogwood species complex (Cornus Subgenus Arctocrania) that contains two diploid species (C. canadensis and C. suecica), their putative hybrids with intermediate phenotypes, and a tetraploid derivative (C. unalaschkensis). Full-length sequences of this gene (∼4 kb) were sequenced and characterized for 47 dwarf dogwood samples representing all taxa categories from 43 sites in the Pacific Northwest. Analysis of nucleotide diversity indicated departures from neutral evolution, due most likely to local population structure. Neighbor-joining and haplotype network analyses show that sequences from the tetraploid and diploid intermediates are much more strongly diverged from C. suecica than from C. canadensis, and that the intermediate phenotypes may represent an ancestral group to C. canadensis rather than interspecific hybrids. Seven amino acid mutations that are potentially linked to myc-like anthocyanin regulatory gene function correlate with petal colors differences that characterize the divergence between two diploid species and the tetraploid species in this complex. The evidence provides a working hypothesis for testing the role of the gene in speciation and its link to the petal coloration. Sequencing and analysis of additional nuclear genes will be necessary to resolve questions about the evolution of the dwarf dogwood complex.     

Sequential flowering of neighboring goldenrods and the movements of the flower predator Epicauta pennsylvanica

Summary As neighboring plants flower sequentially, do flower feeders preferentially remain in the area, rather than move to another area with flowering plants? I examined the movements of the meloid beetle Epicauta pennsylvanica, a flower predator specializing on Solidago, in four types of replicated experimental plots — monocultures of Solidago altissima, or S. altissima interplanted with members of the same genus, same family, or different taxonomic orders. I released marked beetles only in the genus plots, which contained four species of Solidago, two that bloom before S. altissima. The number of beetles in the genus plots declined steadily as S. altissima came into flower in all the plots; the total number of beetles in all the plots remained fairly constant. I found no evidence that plant neighborhoods affected beetle distribution. Beetles foraging on the early blooming Solidago species did not remain in the genus plots as S. altissima came into flower. In addition, beetles that left the genus plots did not differentially accumulate in any of the other plot types, even though one type of plot was a monoculture with four times the density of S. altissima than the other plots.